Quasi two dimensional (2D) and one dimensional (1D) numerical simulations of transient flow with column separation are conducted using the discrete vaporous and gaseous cavitation models (DVCM and ...DGCM) in a simple reservoir-pipeline-valve system. In the quasi 2D transient model, the governing equations are solved by the method of characteristics along the pipe and by finite difference across the pipe cross section to consider the velocity profile, and the final model is coupled with the cavitating models. The comparison between the numerical and experimental results shows that the quasi 2D DGCM is more successful in predicting the maximum head pressures and reproducing the pressure spikes at different water hammer cycles. The quasi 2D model of DGCM correlates better with the experimental data than the quasi 2D DVCM, 1D DVCM and 1D DGCM in terms of pressure magnitude. In sensitivity analysis, the 2D DGCM shows more grid convergence than the 1D models of DGCM and DVCM and 2D DVCM by increasing the number of longitudinal and radial intervals.
•Seawater intruded about 2 km in the coastal region, affecting water resources.•The Taylor diagram indicated that L1 robust is the best inversion method.•The new uncertainty approach indicated a ...considerable variation in seawater intrusion extent.•The BERT reached lower RMS error in less iteration compared to RES2DINV.•Mesh size did not improve the inversion results significantly.
Seawater intrusion (SWI) is one of the most important phenomena which occurs in shorelines and islands and affects groundwater storage in the region. This study aims to investigate how far seawater has intruded in a coastal area and what is its extent variation. The results can lead to different management plans. To achieve these goals, a geoelectrical method is applied in the coastal aquifer of Chaouia, Morocco. In order to choose the best inversion process, different settings are applied in two different software packages namely RES2DINV and BERT and the results are compared using the Taylor diagram. Also, to determine the minimum and maximum SWI extent in the region, a new approach of uncertainty analysis is applied in the inversion process by the Monte Carlo method. The general results indicate that the seawater has intruded about 2 km into the shore. The obtained results show that by considering uncertainty, there is a sensible difference between the maximum and minimum extent of SWI (maximum 9% variation in the area of SWI) which should be noted when doing water research management studies. The methodology procedure in this study can be applied to different coastal areas around the world.
Leachate leakage from landfill sites has become a significant environmental problem in recent years, polluting soil layers and groundwater aquifers. A considerable number of dumpsites near cities are ...operated traditionally and are not designed as landfills, which increases the risk of leakage. Leachate leakage also changes geotechnical and geo-environmental characteristics of soil, often increases soil permeability. Geo-electrical methods are one of the most common methods in leachate leakage investigation in recent years, which are considered as non-destructive methods. Despite recent studies, there are still challenges in applying geo-electrical methods to study leachate leaking from landfill sites that can be addressed through small-scale laboratory studies. One of the critical parameters in the laboratory study of soil resistivity is the voltage of current injected into the soil sample. In this research, the effect of voltage changes applied to the soil samples contaminated by solutions with different contaminant concentrations was investigated. Also, the relation between soil moisture content and resistivity was studied. It was found that there was a sudden change in the reduction rate of soil resistivity for moisture content larger than 13%, which is equal to soil plastic limit. The results showed that by increasing the voltage injected into the soil sample, fluctuation of resistivity values decreased and the transparency of the results increased.
•Laboratory scale resistivity measurement of contaminated soil•Altering injected DC voltage to find the consequences•Altering moisture content and leachate concentration to find the consequences•Increasing injected DC voltage leads to less fluctuation of graphs•Graphs showing the relationship between soil resistivity and its moisture content
Electrical resistivity tomography has potential as a complementary long-term monitoring method in embankment dams; however, the 3D character of the geometry including the shape of the embankment, its ...internal zoned construction and the reservoir water make interpretation challenging. To tackle this problem, a qualified inversion model considering the 3D environment is necessary. In this paper, prior information about the resistivity of different parts of a test embankment dam was used as constraints in order to increase the capability of defect detection in a complex 3D context. Five small defects were incorporated into the core of the model. Laboratory measurements were made on samples of the materials intended to be used for the construction of a test embankment dam, and resistivity values provided from the laboratory measurements were used in the forward modelling. A measurement sequence of around 8000 synthetic data points using extended gradient, crossline bipole-bipole and corner arrays between horizontal-horizontal, vertical-vertical, and vertical-horizontal lines were modelled and inverted all at once. The structural constraints were applied to increase the accuracy of inversion, using the L1 and L2 methods. Different mesh qualities with different boundaries for each region and 3D geometric factor calculation were applied for the inversion to evaluate the effects of region control incorporated in the inversion process. The results showed that L1 and L2 norm inversions combined with region control can determine the location of very small defects and finding the defects located near each other, respectively. Removing the region control from the inversion caused unrealistic resistivity prediction for some regions and the inability to discover the dam defects. Therefore, the proposed methodology can decrease non-uniqueness in the inversion and make time-lapse ERT a valuable monitoring tool that complements other instrumentation techniques and based on these results it was concluded promising to continue with the construction of the test dam using the same type of defects and electrode set-up, for verification under field-conditions.
•Geoelectrical monitoring is a capable tool for damage detection in embankment dams.•Recommendations for use of region control to improve dam defect detectability.•Results of full 3D forward modelling and inversion for zoned embankment dam.•Strategy to be further investigated in the field at Älvkarleby test embankment dam.
Electrical resistivity tomography (ERT) is a potential-based method for detecting internal erosion in the core of embankment dams using the electrodes installed outside. This study aims at evaluating ...the practical capability of ERT monitoring for detecting internal defects in embankment dams. A test embankment dam with in-built well-defined defects was built in Älvkarleby, Sweden, to assess different monitoring systems including ERT and the defect locations were unknown to the monitoring teams. Between 7500 and 14,000 ERT data points were acquired daily, which were used to create the distribution of electrical resistivity models of the dam using 3D time-lapse inversion. The inversion models revealed a layered resistivity structure in the core that might be related to variations in water content or unintentional variations in material properties. Several anomalous zones that were not associated with the defects were detected, which might be caused by unintentional variations in material properties, temperature, water content, or other installations. The results located two out of five defects in the core, horizontal and vertical crushed rock zones, with a slight location shift for the horizontal zone. The concrete block defect in the core was indicated, although not as distinctly and with a lateral shift. The two remaining defects in the core, a crushed rock zone at the abutment and a wooden block and a crushed rock zone in the filter, were not discovered. The results cannot be used to fully evaluate the capability of ERT in detecting internal erosion under typical Swedish conditions due to limited seepage associated with the defects. Furthermore, scale effects need to be considered for larger dams.
A review of one-dimensional unsteady friction models for transient pipe flow SHAMLOO, Hamid; NOROOZ, Reyhaneh; Dept. of Civil Engineering, K.N. Toosi University of Technology, Tehran, Iran, 19697; MOUSAVIFARD, Maryam
Cumhuriyet Üniversitesi Fen : Edebiyat Fakültesi Fen Bilimleri Dergisi,
05/2015
Journal Article
This paper reviews a quasi-steady model and four unsteady friction models for transient pipe flow. One of the factors which may affect the accuracy of the one-dimensional models of transition flow is ...the friction coefficient. This coefficient can be estimated as steady, quasi-steady, and unsteady. In the steady approach, a constant value of the Darcy-Weisbach friction factor is used. In the quasi-steady approximation, friction losses are estimated by using formula derived for steady-state flow conditions. The fundamental assumption in this approximation is that the head loss during transient conditions is equal to the head loss obtained for steady uniform flow with an average velocity equal to the instantaneous transient velocity. During transient conditions the shear stress at the wall is not in phase with the mean velocity. In addition, the velocity profile can be completely different from a uniform flow profile. Therefore friction losses computed by using steady-state relationships are inaccurate in transient laminar and turbulent flow. To cope with this problem, for both laminar and turbulent flows, it is possible to algebraically add unsteady-flow terms to the quasi-steady resistance term of one-dimensional models. Unsteady models are divided into two groups. The first group includes those models which instantaneous wall shear stress is the sum of the quasi-steady value plus a term in which certain weights are given to the past velocity changes. Three models of this group are presented in this paper: Zielke, Vardy & Brown, and Trikha. The second group of models assumes the wall shear stress due to flow unsteadiness is proportional to the variable flow acceleration. Brunone model from this group is presented in this paper. Numerical results from the quasi-steady friction model and the Zielke, Vardy & Brown, Trikha and the Brunone unsteady friction models are compared with results of laboratory measurements for water hammer cases with laminar and low Reynolds number turbulent flows. The computational results clearly show that Zielke model yields better conformance with the experimental data
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